StringStartOrEnd Factory, LinkedQuestion Class and Component, Globe Animation

app/src/apps/Examinations/lib/Examination.js

@@ -26,6 +26,11 @@ class Examination {
   submit() {
     this.submitted = true;
   }
+
+  // Change state of examination to submitted
+  submit() {
+    this.submitted = true;
+  }
 }
 
 export { Examination };

app/src/apps/Examinations/lib/factories/StringStartOrEnd.js

@@ -0,0 +1,138 @@
+import Factory from "../Factory";
+import { MultipleChoiceQuestion } from "../questions";
+
+const MIN_STRING_SIZE = 3;
+const MAX_STRING_SIZE = 16;
+const MIN_ALPHABET_SIZE = 2;
+const MAX_ALPHABET_SIZE = 6;
+const FULL_ALPHABET = "abcdefghijklmnopqrstuvwxyz";
+
+class StringStartOrEnd extends Factory {
+  create() {
+    const content = this.generateQuestionContent();
+    const body = this.generateQuestionBody(content);
+    const options = this.generateQuestionOptions(content);
+    const question = new MultipleChoiceQuestion(body, options);
+    return question;
+  }
+
+  getRandomAlphabetSize() {
+    return (
+      Math.floor(Math.random() * (MAX_ALPHABET_SIZE - MIN_ALPHABET_SIZE + 1)) +
+      MIN_ALPHABET_SIZE
+    );
+  }
+
+  getRandomStringLength() {
+    return (
+      Math.floor(Math.random() * (MAX_STRING_SIZE - MIN_STRING_SIZE + 1)) +
+      MIN_STRING_SIZE
+    );
+  }
+
+  // Generates random string based on the given alphabet and desired string length
+  getRandomString(alphabet, length) {
+    let result = "";
+    for (let i = 0; i < length; ++i)
+      result += alphabet.at(Math.floor(Math.random() * alphabet.length));
+    return result;
+  }
+
+  getSubstrings(strLength, alphabetSize) {
+    // generate available alphabet
+    let alphabet = FULL_ALPHABET.slice(0, alphabetSize);
+
+    // start substring length is at max 2 characters shorter than the total length of the string
+    let startSubstrLength = Math.floor(Math.random() * (strLength - 2)) + 1;
+    // end substring length will depend on the start substring length
+    let endSubstrLength =
+      Math.floor(Math.random() * (strLength - startSubstrLength - 1)) + 1;
+
+    let startSubstr = this.getRandomString(alphabet, startSubstrLength);
+    let endSubstr = this.getRandomString(alphabet, endSubstrLength);
+    return [startSubstr, endSubstr];
+  }
+
+  generateQuestionContent() {
+    const strLength = this.getRandomStringLength();
+    const alphabetSize = this.getRandomAlphabetSize();
+    const [startSubstr, endSubstr] = this.getSubstrings(
+      strLength,
+      alphabetSize
+    );
+    return { strLength, alphabetSize, startSubstr, endSubstr };
+  }
+
+  generateQuestionBody(questionContent) {
+    const { strLength, alphabetSize, startSubstr, endSubstr } = questionContent;
+    let alphabetString = FULL_ALPHABET.slice(0, alphabetSize)
+      .split("")
+      .join(", ");
+    return String.raw`Consider strings of length ${strLength} over the alphabet $\{${alphabetString}\}$. How many such strings are there that start with $${startSubstr}$ or end with $${endSubstr}$?`;
+  }
+
+  generateQuestionOptions(questionContent) {
+    const { strLength, alphabetSize, startSubstr, endSubstr } = questionContent;
+
+    let options = [];
+
+    options.push(this.generateOptionOne(strLength, alphabetSize, startSubstr));
+    options.push(
+      this.generateOptionTwo(strLength, alphabetSize, startSubstr, endSubstr)
+    );
+    options.push(
+      this.generateOptionThree(strLength, alphabetSize, startSubstr, endSubstr)
+    );
+    options.push(
+      this.generateOptionFour(strLength, alphabetSize, startSubstr, endSubstr)
+    );
+
+    options.sort(() => Math.random() - 0.5);
+
+    return options;
+  }
+
+  generateOptionOne(strLength, alphabetSize, startSubstr) {
+    // this generates the number of strings that start with the given substring
+    let result = alphabetSize ** (strLength - startSubstr.length);
+    return {
+      body: String.raw`$ {${result}} $`,
+      correct: false,
+    };
+  }
+
+  generateOptionTwo(strLength, alphabetSize, startSubstr, endSubstr) {
+    // this generates a falsy value that counts strings that start AND end with the given substrings
+    let result =
+      alphabetSize ** (strLength - startSubstr.length - endSubstr.length);
+    return {
+      body: String.raw`$ {${result}} $`,
+      correct: false,
+    };
+  }
+
+  generateOptionThree(strLength, alphabetSize, startSubstr, endSubstr) {
+    // this generates the correct answer
+    let result =
+      alphabetSize ** (strLength - startSubstr.length) +
+      alphabetSize ** (strLength - endSubstr.length) -
+      alphabetSize ** (strLength - startSubstr.length - endSubstr.length);
+    return {
+      body: String.raw`$ {${result}} $`,
+      correct: true,
+    };
+  }
+
+  generateOptionFour(strLength, alphabetSize, startSubstr, endSubstr) {
+    // this generates a falsy value that double counts strings that start AND end with the given substrings
+    let result =
+      alphabetSize ** (strLength - startSubstr.length) +
+      alphabetSize ** (strLength - endSubstr.length);
+    return {
+      body: String.raw`$ {${result}} $`,
+      correct: false,
+    };
+  }
+}
+
+export { StringStartOrEnd };